Comments

The image on line 7 is obviously optional, but makes the plugin fit in with the rest of the search engines. I found it here: http://www.favicon.cc/?action=icon&file_id=19883

Line 8 is where all the work gets done, if you want to customize the search for any particular site, just change the text site:www.gnu.org with your favorite URL, and remove the +info which was just added to help the search narrow down to the info pages.